The present invention related generally to a method of forming interconnectors utilized in the construction of semiconductor device and the like, and more specifically to a method which prevents the oxidation of a substratum layer which provides a barrier metal type effect and enables the process by which an aluminium (Al) type material layer, which buries a connection hole, to be stabilized and to improve the characteristics thereof.
With the recent appearance of VLSI, ULSI etc., the design rules for semiconductor devices have become more stringent, and in order to arrange the interconnectors of substratum and upper layers, the diameters of the connection holes which are opened in the insulating membrane between the substratum and upper layers, have also become more minute, and the aspect ratio has exceeded 1.
The interconnectors of the upper layer is normally formed by sputtering aluminium type material, however with the above mentioned increase in aspect ratio, burying the connection holes so as to adequately achieve the required step coverage, has become more and more difficult event to the point of failing to provide the required connection.
In order to overcome this problem and achieving the desired step coverage, it has been recently proposed to use high temperature sputtering. With this technique, the wafer is heated to a temperature of several hundred degrees in a heating module or the like, while the sputtering process is carried out. This enables the reflow effect to induce the aluminium type material to achieve the required step coverage.
For example, 1989 IEEE/IRPS pages 210-214 discloses an example wherein bore holes having an opening diameter of 1.0 .mu.m are uniformly buried in an Al-2% Cu alloy, and wherein a Ti substratum layer is interposed on a flat wafer surface.
Further, the 38th Applied Physics related League lecture meeting (1991 Annual Spring meeting) Volume 2 page 731 Subject No. 31p-W-7 discloses contact holes having a diameter of 0.25 .mu.m, and an aspect ratio of 4, formed in an interposed 0.05 .mu.m thick polycrystalline silicon layer and which are buried in Al-5% Ge alloy.
In the above, it is explained that a surface reaction occurs between the substratum and Al type layers and improves the burying process. More specifically, the Al type layer which is grown on the upper surface of the membrane which is firstly grown on the flat surface of the wafer, presses forward to the edge portion of the connection holes, and subsequently enters the same. At this time there is nothing in the connection holes, the Al type material layer coats the inner walls of the same. Upon reaching the flat surface of the substratum layer, while a chemical reaction occurs thereat, the Al type material continues to be pulled down into the connection hole until it is completely filled.
If the mechanism via which the burying processes occurs is considered, it is desirable to be able to apply the same to connection holes which have a high aspect ratio.
In connection with the above mechanism, it is an important point, especially with the side walls of the connection holes, whether the wetting characteristics between the substratum layer and the Al type material layer are good, in order that good burying characteristics are achieved.
However, high temperature Al sputtering causes heating of the wafer and has been observed to cause deterioration of the burying characteristics. This is mainly due to the Silicon Oxide (SiO.sub.2) type interlayer insulation membrane becoming heated and releasing moisture and the like and giving off gas. This gas is deemed to contain oxygen in some instance.
This problem is illustrated in FIGS. 1a-1c in an example wherein the substratum layer is formed of Ti.
FIG. 1a shows a wafer which includes a substratum wiring layer 51 formed of a Al type material layer or a silicon base member in which suitable patterns are doped; a SiO.sub.2 interlayer insulating membrane 52 formed using PSG (for example); and a connection hole 52a formed in the SiO.sub.2 interlayer insulating membrane 52 and coated with a Ti barrier metal layer 53.
In order to conduct the high temperature sputtering via which the connection hole 52a can be buried, it is necessary to heat the wafer. This results in the release of moisture (H.sub.2 O) molecular and/or atomic (nascent) oxygen, which is absorbed into the Ti layer 53. As a result, as shown in FIG. 1b the Ti layer becomes partially oxidized and converted into TiOx such as indicated at 53a. The wetting characteristics of Al type layer at such sites is deteriorated.
Under these conditions, as the Al type material layer 54 is formed, a reaction between the Al layer and the TiOx layer 53a inhibits the smooth sliding of the Al layer thereover, and as shown in FIG. 1c, this tends to prevent the connection hole from becoming completely filled and results in the formation of a cavity 55.